A valuable medium handling system 1 includes a communication device 3001 disposed at a storage cassette 31 that is detachably attached to a medium handling device 2 and that stores banknotes, and a controller 513 and a computer 5 that communicate with the communication device 3001 via a communication line 9. The controller 513 and the computer 5 each perform a predetermined process by communicating with the communication device 3001 via the communication line 9.